Hydraulic power brake servo mechanism



March 6, 1951 G. w. PoN'rlus,m I 2,544,042

' HYDRAULIC PowER BRAKE sERvo MECHANISM Filed June 9, 1945 2 Sheets-Sheet 1 INVENTOR.

650/4265 MPM/w51 March 6, 1951 G. w. PoNT|us,111

HYDRAULIC PowER BRAKE sERvo MECHANISM 2 Sheets-Sheet 2 Filed June 9, 1945 ATTORNEY are'deemed unnecessary in the Patented Mer. 6, 1951 HYDRAULIC Mac POWER BRAKE SERVO HANISM George W. Pont-ius, III, South Bend, Ind., as-

signor to Bendix Aviation Corporation, South Bend, Ind., a corporation ol' Delaware Application June 9, 1945, Serial No. 598,491

3 claims.4 (ci. Iso-54.6)

Thisl invention relates to a liquid pressure servo-mechanism of the type which may be used in hydraulic braking systems but not necessarily limited thereto.

An important object of the invention resides in the provision of a uid power unit incorporating a Afollow-up balanced valve means, controlled by an operator, for varying the fluid pressure admitted to one end ofthe power unit, whereby iluid in the other end is put under a unit pressure greater than the unit pressure in said one end of the fluid power unit.

A still further object of the invention is to provide an operator operated hydraulic power unit having a movable piston therein and a sleeve member mounting hydraulically balanced valve means controlled by the operator'for admitting uid to the unit to thereby control movement of said piston. 4

Another important object of the invention resides in the provision of means for use with a servo-mechanism of a hydraulic system comprising a power source and a closed fluid system, for connecting said closed system to the hydraulic power source when said servo mechanism is in normal position to compensate for any change in volume of iluid in the said closed system due to temperature variations.

Still further objects and details of the invention will be apparent from the description hereinafter disclosed and the accompanying drawings illustrating the invention by way of example.

In the drawings: Figure 1 is a diagrammatic illustrationpartly in section of a hydraulic system comprising a servo-mechanism according to the invention;

Figure 2 is an enlarged longitudinal section of the piston `o f` the servo-mechanism showing the make-up valve in closed position; and

Figure 3 shows a longitudinal section of a modication of theservo-mechanism.

Referring now to Figure l, the numeral I0 indicates a reservoir to which is connected a pump I2 which receives fluid from the reservoir and puts the same under pressure in an accumulator I4 which is connected to the pump through a regulating or unloading valve I6, of any conventional design. A hydraulic power unit or servo mechanism I8 is connected to the unloading valve I6 and accumulator I4 through pipes 20 and 22. A pipe 24 connects the servo mechanism to the reservoir I8, and pipes 26 and 28 connect the mechanism with Amotors 30 vof brakes 32. A conduit 34 connects the unloading valve I6 to pipe 24 which joins the reservoir to by-pass fluid thereto when the accumulator pressure has reached a predetermined value dependent upon the setting of the unloading valve I6. Since the unloading valve per se. forms'no part of this invention its details of construction and operation present specification.

with the chamber 82.

. 2 The servo-mechanism I8 comprises a cylinder 36 which in the instant case is vformed of two axially displaced casings 38 and 40, having anged portions 42 and`44 respectively, constructed and arranged to receive bolts 46 which securely` hold the casings in xed relationship.

yThe casing 48, which forms one end of the cylinder 36, has a flange 48 integral therewith andconstituted to be fastened to some part of a vehicle, not shown. with which the servomechanism is. associated. An outlet port 58 is formed in the casing 40 Vof the cylinder and is connected to the pipe 24 which communicates with the reservoir. A working port 52 is disposed in the casing 38 at the other end of the cylinder and is constructed and arranged to receive the pipe 26 to communicate said other end of the cylinder with the motors 38 of brakes 32. Also formed in the casing 38 is an inlet port 54 threaded at 56 to receive the pipe 20 which suppliesfluid under pressure from theV accumulator I4 to the cylinder 36.

Reciprocally contained within the cylinder 38 of the servo-mechanism is a piston 58 normally urged toward one end of the cylinder by a spring 60. The piston 58 has a circumferential groove 62 extending axially along the piston between lands 64 and 66 each of which has an annulus 68 and 'Io formed therein respectively to receive seals 'I2 intended to isolate the inlet pressure in groove 62 from chamber 'I4 in one end of the cylinder and 'chamber 16 in the other end of the cylinder. Piston 58 is bored longitudinally at 88 to intersect a chamber 82 which is incontinuous communication with the inlet 56 through the circumferential groove 62. This circumferential groove permits chamber 82 to be subjected to inlet pressure at all times irrespective of the position of the piston in the cylinder. A valve seat 84 is formed at the intersection of the bore 80 A boss 86 formed in the cut-out portion 88 of the piston provides means for retaining one end of the spring 68 in place against the piston. The other end of the spring is retained in a boss 89 counterbored at 90. The boss 89 also provides a stop for piston 58 when it is moved to the left end of the cylinder.

For controlling the inlet pressure to chamber 'I4 in one end of the cylinder, means carried by the piston is provided. Said means comprising a valve 92 reciprocably disposed in the bore 80 and normally urged against the valve seat 84. The

l, valve 92 includes a stem 94 of the same diameter as bore 80, an extension 96 of the stem having a diameter the same as bore 8o to form a bearing t therewith, and a frusto-conical valve head 88 and a valve head Illu, the former of the valve heads being arranged to engage valve seat 84. A longitudinal passage IIl2 connects the ends of the valve 92 to permit the same pressure to acton the ends of the valve whether opened or closed. The bore extends into the boss 86 to form a of a spring |04 which abuts one end of the valve 02 to normally urge the frusta-conical head 98 onto seat 84. An annulus 91 in the stem extension 06 is constituted to receive a seal 00 to divorce chamber 82 from the end oi.' bore 80 in which spring 86 is disposed.

Since that part of the system connected to the working port 52 and including chamber 16, pipes 26 and 28, and motors 30 is a closed hydraulic system, means must be provided to compensate for any change in volume of uid in that part oi the system due to temperature variations of the iluid. This type of system must be protected against expanding uids due to rising temperatures and against shrinking fluids due to decreasing temperatures, the latter of which will have a tendency to form a vacuum in the system. Referring to Figure 2. the means employed for meeting these conditions include a valve mechanism which comprises passages |40 and |42 drilled in piston 68 to connect chamber 14 to chamber 16. Passage |42 is interiorly threaded at |44 to receive a bushing `|4| drilled at |48 to the proper size to permit a valve stem |50 to slide therein. The bushing is drilled at |5| to connect passage |40 to passage |42. Passage |42 is countersunk at |53 to preclude the closing of passage |5| when the bushing |46 is bottomed. One end of the valve stem has a cone-shaped valve head |52 integral therewith and the other end of the stem is equipped with a threaded portion |54 onto which is threaded a nut |56 having a ilange |58 against which abuts one end of a spring |60, the other end of which abuts the bushing |46. lThe spring |60 normaly urges the valve head |52 against a valve seat |52 to close the passages |40 and |42. The threaded portion |54 of the valve stem protrudes beyond the right end of piston 58 so as to engage a recessed portion |64 of casing 40 when the piston is in its normal position to the right end of the cylinder-to unseat the valve head |52 from seat |62. Under normal conditions of operation the pressures acting on opposite sides of valve head |52 are equal and the valve is held onto its seat |62 by spring force only.

Operator operated means is provided for controlling valve 92 and comprises a piston |06 having an axis of reciprocation substantially coincident with the axis of reciprocation of piston 58. Piston |06 is movable relative to piston 58 and has a cirfumferential groove |08 axially disposed between lands ||0 and ||2. 'I'he lands have annuluses ||4 and ||6 formed therein respectively to receive seals ||8. The seal disposed in the annulus ||4 divorces groove 08 from chamber 14 and the seal disposed in annulus ||6 divorces groove |08 from atmosphere. The piston |06 is bored longitudinally at and radially at |22. A valve seat |23 is formed in the bore |20 where it terminates in one end of the piston |06. The bore 80 and valve head |00 have substantially the same diameters. The radial bore |22 intersects the groove |08 and the bore |20. The circumferential groove |08 is always in communication with the outlet port 50 irrespective of the position of the piston. 'I'he piston |06 is recessed at |26 to receive one end of a thrust member |28 which is pivotally fixed at |30 to a foot lever or treadle |32 pivotally fastened at |34 to a vehicle, not shown.

The valve 92, is carried by the piston 58 and is disposed therein so that the valve heads 88 and |00 seat on the valve seats 84 and |23 respectively. The bores |20, |22 and groove |08 form a passage connecting chamber 14 to outlet'50. The bore 80,

chamber 82 and groove 62 form a passage connecting the inlet 54 to the chamber 14. Valve 92 is normally seated in the passage connecting the inlet port to chamber 14 and normally unseated in the passage connecting the outlet port 50 to chamber -14.-

Figure 3 illustrates a modified embodiment of the device of the invention and comprises a cylinder 200 having an end cover 202 with a iiange 204 and a tubular portion 206. The end cover 202 is secured to the cylinder 200 by bolts 208 which pass through openings 2|0 in the flange and engage interiorly threaded bores 2|2 of the cylinder. The interior of the cylinder 200 is stepbored at 2|4 and 2|6 to accommodate a piston 2|8 having a minor diameter 220 and a major diameter 222. The piston is normally urged toward one end of the cylinder. the right end as viewed in Figure 3, by a spring 223 which has one of its ends abutting the cylinder and the other end abutting the piston. The piston is provided with a circumferential groove 224 intermediate the two diameters. Annuluses 226 and 228 are located in the minor and major diameters respectively for receiving seals 230 and 232 which sepa-v rates the cylin'der into three chambers 234, 236 and 236, located on the left of the piston, circumferentially thereof and on the right of the piston respectively. Chamber .234 is continuously in communication with the motors of the brake system of Figure 1. A working port 240 opens into chamber 234 and connects that chamber to the motors. The chamber 234 and its connections to the motors 30 form a closed hydraulic system in the same manner as the corresponding parts in Figure 1. Chambers 236 and 238 are normally connected to reservoir through an outlet port 242 disposed in cylinder 200. An inlet 244 is formed in the e'nd cover 202 and connects the accumulator |4 to the chamber 238 at times. The tubular portion 206 of the end cover contains a groove 246 formed between lands 248 and 250 having annuluses 252 and 254 respectively. A sleeve 256 having one end extending into chamber 238 and the other end protruding beyond the tubular portion 206 is arranged to slide on the lands 248 and 250. The annuluses 252 and 254 are formed to have seals 258 placed therein for isolating groove 246 from atmosphere and from chamber 238. A passage 260 in the end cover connects the inlet 244 to the groove 246. Sleeve 256 has a longitudinal passage 262 therein and radially drilled holes 254 and 266 axially spaced in said passage for transmitting uid from the inlet to a chamber 239. The radial holes 264 are disposed within the sleeve to communicate the longitudinal passage to the inlet irrespective of the position of the slidable sleeve which is slidable relative to the piston 2| 8. The sleeve is operator operated by any suitable means such as the foot treadle |32, shown in Figure 1, having the necessary linkage, not shown, connecting the lever to a thrust member 268.

For controlling the inlet iiuid pressure in chamber 238 valve means is provided which is actuated by movement of sleeve 256. This valve means is carried by that portion of the sleeve which extends into one end of the cylinder and comprises a tubular member 210 enveloping the extended portion of the sleeve. The tubular member 210 has an inturned ange 212 which is secured to the sleeve 256 adjacent the radial holes 266. The flange 212 spaces the tubular member radially from the sleeve to thereby provide the chamber the seat 214 by a ,spring 218V, to control the inlet fluid pressure from chamber 239 to chamber 238.

A passage 280 connects the circumferential groove 224 of piston 2|8 to a chamber 282 of the piston.

A disc-like member 284 is mounted adjacent chamber 282 and forms one wall of the chamber. The disc-like member is provided with a valve. seat 286 disposed with respect to the .valve 216` to be engaged thereby to control communication between the reservoir and chamber 238. Member l5 284 has a slight radial displacement with respect to the piston 2I8. An element 281 is secured to the piston and forms a stop to limit the axial movement of member 284. A seal 289V prevents leakage between the chambers 282 and 238 when valve 216 is seated at 286. With this arrange-l ment of the valve seat 286 valve head 290 of valve 216 tends to seat squarely therein. That is, the seal 289 may be deformed according to the force at the points of contact of valve head 290 on valve seat 286. This is conducive to a substantially uniform seating of the valve head 290 over seat 286. Valve 216 has a conical portion 288 formed therein to engage valve seat 214 and a l second conical portion 290 constituted to engage valve seat 286. The sleeve 256 is provided with a diameter D which is greater than diameter D' of the valve head 290 so that when valve 288 is off valve seat 214 the pressure in chamber 238 acts on annulus D-D' urging sleeve 256 to the right. 35 Y This action or reaction of the pressure in chamber 238 on the end of sleeve 256 provides feel" for the operator. The feel is proportional to y the force exerted by the o perator. Tubular mem-l ber 210 is lprovided with stop elements 292 and 294 40 axially spaced exteriorly of the member and fixed thereto in a manner to be engaged by .washer-like elements 296 and :.298 respectively, urged thereagainst by a spring 300. The washer-like element 296 is arranged on the tubular member 210 to engage the piston at 302 to hold the element from axial movement with the tubular member as sleeve 256 is moved to the left as viewed in Figure 3 to thereby compress spring 300. Furthermovement of the sleeve to the left will seat the valve head 290 on the valve seat 286 and unseat the valve head 288 from valve seat 214. Any further movement of the sleeve member will cause the end of the tubular member to engage the disclike member 284 to limit the leftward movement of the operator operated means. Radially disposed holes 304 adjacent 4the end of tubular member 210 permit the free passage of fluid past valve seat 214 when the end of the tubular member in which the holes are located abuts the disc-like member 284.

To compensate for a change in the volume of]V iluid in the chamber 234 and in the closed part ofthe system due to temperature variations piston 2|8 is drilled at 3|0 and 3|2 to provide com- 65 munioation between chambers 234 and 238 at times. The drilled passage 3|2 is "interiorly threaded to engage an exteriorly threaded bushing 3 I 4 having a drilled passage 3 6 therein counterbored at 3 I8 and 320 to form a valve seat 322. 70 A ball valve 324 is forced toward seat 322 by a spring 326. A pin 328 is loosely flt into the pas-V sage 3|6 and has one end abutting the ball valve and the other end abutting the end cover 202 vto unseat the ball valve when the piston 2|8 is nor- 75 mally positioned in ure-3. u.

Since the principle of operation of the mechanisms of Figures 1 and 3is similar, the operation of Figure 1 only will be described. -However, it should be noted that the device'in Figure 3 is a booster type hydraulic unit'. Thatiis, the prescylinder 200, as shown in Figsure at port 240 is greater. than the inlet pressure at port 244. This pressure difference at the two ports may be varied. as requiredr by changing the ratio of the diameters 220 and 222V of the ends ofpiston2|8.

The `operation of thev servo-mechanism is as follows: With the parts ofthe servo-mechanism or powerunit in the positions` shown in Figure 1 the inlet fluid pressure isacting'infgroove 62, chamber 8 2 and on valvehead 98.` Since bore 80 is of the same diameter on'either side of valve head 98, valve 92 is balanced'to inlet pressure and is heldv on seat 84 by the force only of spring |04. Valve 92 is therefore closed to the admission of inlet fluid pressure to chamber 14. Valve head |00 ofthe valve 92 is unseatedfrom seat |23 to communicate chamber 14 to reservoir through the passages |20, |22 and the outlet-port 50. Chamber 16 is under the same pressure as chamber 14 since under the above. assumed conditionsvalve head .|52 is unseated from seat |62 to establish communication between the chambers. That is, with the piston 58vin its normal position, at .one end of the .cylinder lthe threaded portion |54 of valve stem |50 abuts the recessed portion |64 of casing 40v to unseat valve head |52.

To operate thefbrales 32, the treadle |32 is depressed, that is, rotatedto the left. .This moves piston |06 into contact with valve head `|00 to seal offchamber-M .to reservoir. .Continued rotation of the treadlerunseats valve head 98 to admit inlet fluid pressure to chamber 14 to move piston 58 to the left, toward the other end of the cylinder. Movement of piston 58 to the left displaces the fluid in chamber 16 which is connected to the motors 30, through the working port 52 and pipes 26v and 28. Because of the equal areas of the ends oflpiston 58 .the pressure in chamber 16 will be made substantially equal to the pressure in chamber14 minus the force of loading spring 60 neglecting friction. The pressure in chamber 14 acting to move piston 58 tothe left is also effective on the left end of the piston |06 tending to move it to the right/against the force applied to the treadle by the operator. Manifestly this treadle pressure is going tovary directly with the fluid pressure acting in motors 30. This relationship of treadlepressure to iluid motor pressure may be varied by `chang ing the area of piston |06. It will be noted that.unseat ing valve `head 98 to radmit fluid .under. pressure to chamber 14 moved piston 5.8..r ,direction to reseat valve head 98 to cut off fluir, pressure .to the chamber 14. So long asvthetre'adle ypressure is equal to the sum of the combined hydraulic reaction acting on the end of piston |06 and the load of spring |04, the pressure inthe chambers will remain substantially unchanged. If the treadle 'pressure is in excessof the hydraulic reaction and the load of spring |04, the piston 58 will continue to vmove leftward until the pressure in chambers 14 and 16 are equal to the accumulator pressure of the system. A decrease in the treadle pressure below the hydraulic reaction and load of spring |04 will unseat valve head |00 to connect chamber 14 to .reservoir to reduce the pressure in chambers 14 and 16.V

Since the pressures existing on both sides of piston 68 in chambers 14 and 16 are substantially the same under normal operating conditions, it follows that the pressures acting across the head |62 when it is seated on valve seat |62 are likewise substantially equal. This normal balanced condition across head |62 coupled with the proper arrangement of the valve head in the piston provides an emergency valve which may be operated in the event of any loss of fluid in chamber 16 to admit accumulator pressure directly to the motors. That is, the loss of iluid in chamber 16 will cause an unbalanced pressure in chambers 14 and 16, with the greater pressure in chamber 14 acting to unseat the valve head |62 against spring |60 to admit iiuid to chamber 16 and to the motors 30.

It for any reason the hydraulic power should fail, the brake system may be put under pressure by an operator. That is, with the hydraulic power cut oil? depressing treadle |32 transmits a force through piston |06 and valve 92 to piston 68 to thereby move the latter in a direction to put the-duid in chamber 16 under pressure.

I claim:

1. A iiuid power unit comprising a cylinder, a piston in the cylinder dividing the same into opposed chambers and normally urged to one end of the cylinder, the chamber in the other end of the cylinder being formed to receive the piston to thereby put fluid in said chamber under pressure, an inlet port in the cylinder, an outlet port in the cylinder normally in communication with said one end of the cylinder, a working port in the cylinder in continuous communication with the other end of the cylinder, a passage in the piston 'connecting the outlet port to said one end of the cylinder, operator operated means slidably disposed in said one end of the cylinder and including a sleeve member having a portion extending into said one end of the cylinder and a portion protruding exteriorly of said cylinder, a

passage through said sleeve for communicating said one end of the cylinder witn the inlet port,

` valve means for controlling communication between said inlet and outlet ports and said one end of the cylinder and including a valve seat in each passage, a valve member carried by that portion of said sleeve extending into said one end of the cylinder and having one end formed to engage the valve seat in the passage of said sleeve Ato thereby cut oil communication between said inlet and said one end of the cylinder and the other end of said valve member being formed to engage the` valve seat in the passage of said piston, a spring normally urging said valve member onto the valve seat in the passage of said sleeve, and means supported by said sleeve for urging the same in a direction to unseat said other end of the valve member from the seat in the passage of said piston to thereby communicate said outlet port with said one end of the cylinder, said valve member being formed so that equal eiective areas are exposed to the outlet port and to the inlet port at all times regardless of the position of said valve member.

2. A fluid power unit comprising a cylinder, a piston in the cylinder dividing the same into opposed chambers and normally urged to one end of the cylinder, the chamber in the other end of the cylinder being formed tov receive the piston to thereby put fluid in said chamber under pressure, an inlet port in the cylinder, an outlet port in the cylinder normally in communication with said one end of the cylinder, a working port in the cylinder in continuous communication with the other end oi' the cylinder, a passage in the piston connecting the outlet port to said one end of the cylinder, operator operated means slidably disposed' in said one end o! the cylinder and including a sleeve member having a portion extending into said one end oi.' the cylinder and a portion protruding exteriorly of said cylinder, a passage through said sleeve for communicating said one end of the cylinder with the inlet port, valve means for controlling communication between said inlet and outlet ports and said one end of the cylinder and including a valve seat in each passage, a valve member carried by that portion of said sleeve extending into said one end of the cylinder and having one end formed to engage the valve seat in the passage of said sleeve to thereby cut of! communication between said inlet and said one end of the cylinder and the other end of said valve member being formed to engage the valve seat in the passage of said piston, a spring normally urging said valve member onto the valve seat in the passage of said sleeve, and a spring interposed between said piston and sleeve for urging the same in a direction to unseat said other end of the valve member from the seat in the passage of said piston to thereby communicate said outlet port with said one end of the cylinder, said valve member being formed so that equal eective areas are exposed to the outlet port and to the inlet port at all times regardless of the position of said valve member, the end of said sleeve extending into said one end of said cylinder having an effective area such that when said valve member is seated in the passage of said piston and unseated in the passage of said sleeve the pressure in said one end of the cylinder acts on said effective area of the sleeve to thereby urge the same in a direction opposing movement of said sleeve by the operator and with a force proportional to the operators applied force.

3. A device as claimed in claim 2, wherein a valve device is carried yby the piston to be operated when said piston is at said one end of the cylinder to establish communication between said one end and the other end of the cylinder to compensate for change in volume of iuid in said other end of the cylinder due to temperature variations of the iiuid.

,GEORGE W. PONTIUS, III.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,604,545 Bragg Oct. 26, 1926 1,831,737 Broussouse Nov. 10, 1931 1,938,979 Sawtelle Dec. 12, 1933 1,991,902 Lloyd Feb. 19, 1935 2,185,449 Veenschoten Jan. 2, 1940 2,266,504 Main Dec. 16, 1941 2,318,756 Chouings May 11, 1943 2,385,942 Rockwell Oct. 2, 1945 2,413,380 Rush Dec. 31, 1946 FOREIGN PATENTS Number Country Date 384,678 Great Britain Dec. 9, 1932 549,300 Great Britain Nov. 16, 1942 747,273 France Mar. 28, 1933 

